To prevent health care workers who handle used hypodermic needles from contracting AIDS or hepatitis or the like through an accidental needle prick, it would be desirable to have incorporated into the design of single use needles a guard which would automatically enclose the needle tip when the needle is withdrawn. Thus health care workers would be protected as would anyone else who might accidentally come in contact with a contaminated needle before it has been properly disposed of or recycled. This would include medical personnel who must draw blood in order to determine the presence of infectious disease. Also it would be more difficult for drug abusers to reuse a single use needle equipped with such a guard.
Obviously it would be important that such a guard not interfere with the operation of the needle to a significant extent and be as simple and low cost as possible yet still work entirely automatically such that no further action beyond insertion of the needle and withdrawal be required of the operator. If activation of the guard were on an elective basis, in many cases it would simply not be used. Also, manual activation complicates usage and requires further manipulation which itself could be dangerous. The guard must also be fail safe so that the needle cannot puncture the guard even when very high pres sure is applied.
The prior art reveals a great variety of needle guards, but all fall short of achieving the objects of this present invention. Many early guards (1960's and 1970's) themselves created a danger by requiring the operator to manually force the guard in such a manner that accidental puncture could result. Also many were not fail safe. Pressure on the end of the needle guard could cause penetration by the needle tip.
More recently issued patents show technology which alleviates many of the problems, but still does not satisfy all the objectives of this invention. The Self-capping Needle Assembly of Dombrowki and Welch, U.S. Pat. No. 4,790,828 (1988), shows tip guards which do not require motion toward the sharp tip to activate (thus reducing danger to the operator) and have one way gates entrapping the tip once the guard is in place. However, they do require the operator to supply the force for positioning the guard after needle use and the guards occupy a substantial portion of the needle shaft in their initial position, possibly dictating the use of a longer needle than normal. One version is not fail safe because the guard can be easily pulled off the end of the needle. In all versions the sharp tip can come in contact with and possibly puncture the end of the guard unless the guard is fabricated from a substantially stout material, which would increase cost and detract from feasibility.
Vaillancourt shows an embodiment of his Post-injection Needle Sheath (U.S. Pat. No. 4,725,267) which eliminates the need for the attendant to supply the physical force necessary to place the guard by employing a compression spring for positioning. However, the guard is not automatic. The attendant must still push or turn a mechanism to initiate operation of the spring. The guard is not completely fail safe because it is possible to position the guard such that the needle could escape. Also, even with the guard positioned to entrap the needle the sharp point can easily come in contact with the end of the cap and perhaps pierce it should it be subjected to a sudden accidental extreme pressure.